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Germs and Shoes: Is There Trouble Afoot?

It should come as no surprise that the bottom of our shoes have a hodgepodge of germs attached. Several studies have come out over the years that not only confirm that, but may make you want to think twice about how you handle your shoes and whether you want to traipse through your house in them.

Dr. Charles Gerba, professor of microbiology, immunology, environmental science, and other topics at the University of Arizona, studied the germs collected on footwear and the role of shoes in the movement of bacteria from contaminated floor spaces to other surfaces, and the results were eye-opening.

“If you wear shoes for more than a month, 93 percent will have fecal bacteria on the bottom of them,” he told NBC’s “TODAY” about his findings. He blames pet waste on the ground and whatever splashes out of toilets and onto public restroom floors for this contamination. So there’s the straight poop.

Upping the “eww” factor, the study found large numbers of bacteria both on the bottom and inside of shoes, including Escherichia coli (E. coli). Although most varieties of E. coli are harmless or cause relatively brief diarrhea, according to the Mayo Clinic, a few particularly nasty strains can cause severe abdominal cramps, bloody diarrhea, and vomiting. Scientists also found Klebsiella pneumonia, a common source for wound and bloodstream infection as well as pneumonia; and Serratia ficaria, a rare cause of infections in the respiratory tract and wounds.

Another study conducted by the University of Houston College of Pharmacy and the Department of Microbiology at Montana State University sampled multiple households in Houston for the presence of Clostridium difficile (C. difficile), a bacterium with a long lifespan that commonly causes bowel problems like diarrhea. The researchers found that shoes harbored more C. difficile than even the surface of a toilet.

But does the average person really need to worry much about the risk? Not really, says Dr. Kevin Garey, the author on the C. difficilestudy and professor at the University of Houston College of Pharmacy. He told Live Science, “For a healthy individual, bacteria on shoes likely pose no or minimal risk.” However, those at risk of infection and people with compromised immune systems or allergy issues may want to take extra precautions. And if you have a small child that will be crawling around on the floor, you should consider removing outdoor shoes before coming inside your home.

Researchers found that simply washing footwear according to manufacturer’s instructions reduced all bacteria by 90 percent or more, but it’s unlikely any of us is going to wash our shoes before wearing them inside. Experts say cleaning your shoes periodically, keeping them out of the main living area, and keeping dust (which is food for bacteria) to a minimum all helps. Or you might just consider slipping into a pair of clean, cozy slippers before entering the house.